GB2253097A

GB2253097A - Electrical contacts.

Info

Publication number: GB2253097A
Application number: GB9202055A
Authority: GB
Inventors: Robin Bose
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 1991-01-31
Filing date: 1992-01-31
Publication date: 1992-08-26
Anticipated expiration: 2012-01-31
Also published as: GB9202055D0; GB9102062D0; AU659436B2; WO1992014282A1; GB2253097B; AU1201892A; CA2101558A1; EP0569433A1

Abstract

The electrical terminal pins of a cordless electrical appliance may be implicated in electrical switching operations and, to increase their longevity, they are formed of copper or a copper alloy having a thermal conductivity approaching that of copper and are provided with a plating of from 30 to 40 mu m thickness of silver containing from 0.3 to 0.7 % antimony.

Description

IMPROVEMENTS RELATING TO CONDUCTORS FOR ELECTRICAL SWITCHING APPLICATIONS Field of the Invention: This invention generally concerns improvements relating to conductors for electrical switching applications.

Background of the Invention: In many electrical switching applications, discrete contacts formed for example of silver or a silver alloy are utilized to provide reliability and longevity in the switching operation. However such an approach is frequently inconvenient from a manufacturing viewpoint and can give rise to unacceptable cost. Electrical appliances, for example electrically heated water boiling vessels, particularly of the cordless type, are also known in which the power supply terminal pins of the appliance are implicated in switching operations. Commonly such terminal pins are formed as brass stampings, but brass pins are susceptible to excessive wear in applications involving frequent or relatively frequent switching operations, such wear arising on account particularly of arc erosion.To reduce this problem it is known to silver plate the brass stampings but this does not provide a satisfactory solution.

Summarv of the Invention: According to one aspect of the the present invention there is provided a preferred form of electrical conductor for electrical switching applications in which electrical contact to the conductor is repeatedly made and broken in use, such conductor providing excellent electrical characteristics in combination with superior wear characteristics and comprising a member formed of copper or of a copper alloy having a thermal conductivity approaching (eg. at least 90%) that of copper, said member being provided with a thick plating layer of silver and antimony.

According to another aspect of the present invention there is provided an electrical conductor for electrical switching applications in which electrical contact to the conductor is repeatedly made and broken, said conductor being formed of brass and having a thick plating layer thereon of silver and antimony.

The above and additional features of the invention are set forth with particularity in the appended claims and will be best understood from consideration of the following detailed description of an exemplary embodiment which is given with reference to the accompanying drawing.

Brief Description of the Drawing: Figure 1 is a schematic side view, partly in section, showing an X12 element protector control as manufactured by Otter Controls Limited fitted to a water heating vessel, and showing a co-operating CS2 connector part also as manufactured by Otter Controls Limited for incorporation into the base unit of a cordless appliance, the X12 control and the CS2 connector part of the base unit being shown spaced apart from each other one above the other; and Figure 2 shows the X12 control and the CS2 connector part shown in engaged condition.

Detailed Description of the Embodiment: A description will first be given of an exemplary cordless connection system to which the present invention may advantageously be applied, the system in question being described and illustrated in greater detail in European Patent Application No. 91300780.3 (published as EP-A-0441536) of Otter Controls Limited.

Referring first to Figure 1, an X12 device is designated 1 and a co-operating CS2 base unit connector part is designated 2. The X12 device 1 is substantially as described in GB-A-2194099 with reference to Figures 3A, 3B and 3C thereof, and as shown in Figure 1 hereof is attached in conventional manner to a side wall of a schematically-illustrated water heating vessel 3. As is described in GB-A2194099, the X12 device has the function of interrupting the supply of electrical power to a heating element within the vessel 3 in the event of an element overtemperature condition occurring, for example as a result of the vessel being powered without there being any water in it. The means whereby this protective function is achieved is not especially material to the present invention and will not be described further herein.All that need be said in this regard is that the X12 device 1 has live, neutral and earth terminal pins 4, 5 and 6 within a hooded or open-based socket inlet shroud 7 and incorporates within the body of the device thermallyresponsive switch means for interrupting the electric circuit from the live and neutral pins 4, 5 to the vessel heating element in the event of an element overtemperature condition.

The physical arrangement of the terminal pins of the X12 device and of the socket inlet shroud is fully conventional and enables the vessel 3 to be used in a corded manner, if desired, with a standard 10 amp kettle type connector plug (not shown) plugged into the socket inlet shroud 7 and making contact with the terminal pins. This arrangement is adapted also to enable the vessel to be used in a cordless manner with a base unit incorporating the illustrated connector part 2 as will now be described.

The connector part 2 comprises a moulded plastics upstand from the base part of the appliance which is shaped to mate with the socket inlet shroud 7 of the X12 device 1 when the vessel part of the appliance is set down onto the base. Although not illustrated in the drawing, it will be understood that the vessel and/or the base part of the appliance may include formations designed to ensure proper mating of the connector part 2 with the socket inlet shroud 7 of the X12 device 1 when the vessel part is seated on the base.Within the connector part 2 there is provided a moulded plastics shutter 8 which is spring biassed towards a closed position by means of a coil spring 9, and three leaf-spring terminals 10, 11 and 12 which couple within the base unit 2 to the live, neutral and earth conductors of a power supply cord and are adapted to contact the live, neutral and earth terminal pins 4, 5 and 6 respectively when the vessel part 3 is seated upon the base and the shutter 8 is displaced to an open position as shown in Figure 2.

In accordance with the teachings of the present invention, a preferred form of terminal pin providing excellent electrical characteristics in combination with superior wear characteristics comprises a copper pin, or a pin formed from a copper alloy having a thermal conductivity at least 90% that of copper, provided with a thick plating layer of silver and antimony, and the terminal pins 4, 5 and 6 can advantageously have this construction. If a common brass pin with a 5 micron layer of essentially pure silver plating were to be used then the life of the contact effected by the pin to the base unit connector springs would be around 1000 cycles of connection and disconnection. This may be increased to around 5000 cycles by use of a plating of 40 microns of essentially pure silver. This life may further be increased by use of a pin made from copper or a high thermal conductivity copper alloy, but a side effect would be the formation of silver powder caused by abrasion of the contact surfaces which could lead to premature electrical breakdown. By the use of a thick plating (e.g. at least 30 microns and preferably 40 microns thickness) comprising silver with a small amount of antimony, typically about 1% and particularly between 0.3% and 0.7%, on a pin formed of copper or a high thermal conductivity copper alloy, the formation of silver powder is inhibited and a life of about 70,000 cycles may be obtained.

A silver antimony plating may be used to improve the performance of a brass pin, and a copper or high thermal conductivity copper alloy pin also obtains improved performance as compared to a brass pin, but the best results are obtained in accordance with the teachings of the present invention when these two improvements are combined. Accordingly the preferred form of terminal pin for co-operation with a base unit connector as herein described is a pin formed of copper or of a copper alloy having a thermal conductivity at least 95% and preferably 99% that of 99.95% pure copper, and having a plating layer of at least 30 microns and more preferably 40 microns thickness comprising fine silver (99.9% purity) with the addition of about 1% and more preferably between 0.3% and 0.7% of antimony.

The invention having been described in the foregoing with reference to an exemplary application, it is to be well appreciated that other applications for the invention are possible. Furthermore, modifications could be made to the described arrangement, for example by providing the leaf spring terminals 10, 11 and 12 in the connector part 2 with a thick silver-antimony plating in accordance with the invention or with silver contact pads.

Claims

CLAIMS:

1. An electrical conductor for electrical switching applications in which electrical contact to the conductor is repeatedly made and broken, said conductor comprising a member formed of copper or of a copper alloy having a thermal conductivity approaching that of copper and said member being provided with a thick plating layer of silver and antimony.

2. An electrical conductor as claimed in claim 1 wherein the thickness of said plating layer is at least 30 microns.

3. An electrical conductor as claimed in claim 1 or 2 wherein the silver antimony plating contains about 1% antimony.

4. An electrical conductor as claimed in claim 3 wherein the silver antimony plating contains between 0.3% and 0.7% antimony.

5. An electrical conductor as claimed in any of the preceding claims configured as a terminal pin.

6. An electrical switch incorporating at least one electrical conductor as claimed in any of the preceding claims.

7. An electrical appliance incorporating an electrical switch as claimed in claim 6.

8. An electrical appliance as claimed in claim 7 and wherein a power supply terminal pin of the appliance is implicated in switching operations and said power supply terminal pin constitutes said electrical conductor.

9. An electrical conductor for electrical switching applications in which electrical contact to the conductor is repeatedly made and broken, said conductor being formed of brass and having a thick plating layer thereon of silver and antimony.